My opinion, voiced in the First impressions topic:
And I agree with you on the sound being a bit dull, but I think that it stems from the device being new and not having played enough. What I always do when finding the sound dull, is let the device play lots of sound before judging:
I did find an app called Pink Noise on the Play Store that’s playing now on my Fairphone. From my experience with other device, it might take a full 24 hours of playing lots of different music or a few weeks of playing the device now and then, for the higher frequencies to sound well (I didn’t have access to pink noise, though what I would sometimes is play the radio without any station picked up, just the noise).